Rotary motion detector with signal device



March 1968 N.J. RYSKAMP 3,372,256

' ,ROTARY MQTION DETECTOR WITH SIGNAL DEVICE Filed Ju ly 27, 1966 United States Patent 3,372,256 ROTARY MOTEON DETECTOR WITH SIGNAL DEVECE Neil J. Ryskamp, Markham, Ill., assignor to Ailis- Chalmers Manufacturing Company, Milwaukee, Wis.

Filed July 27, 1966, Ser. No. 568,158 1 Claim. (Cl. 200-82) ABSTRACT OF THE DISCLOSURE A rotary motion detector for sensing movement of a moveable part utilizing in combination a hydraulic actuator and positive displacement pump.

This invention relates to a control system for sensing movement of a movable part, and transmitting a signal in response to such movement and, while not limited to such specific application, is particularly adapted for insuring safe operation of a gripping type attachment for a lift truck.

In this type of truck the load is clamped between jaws or arms pressed toward each other by suitable means such as fluid pressure motors, and it is important that the clamping pressure he maintained at all times when the truck is in motion so that the load will not be inadvertently dropped, with possibie danger to the operator, and practically certain damage to the load. These considerations apply whichever direction the truck is moving. Since the clamping pressure is under the control of the operator by means of a control valve, there is always the possibility of his unintentionally actuating the valve in a manner to drop the load while the truck is in motion. Prior art rotary motion responsive switches have not proven entirely satisfactory in reliability and sensitivity for use in automatic controls for blocking release of clamps of lift trucks such as shown in F. C. Schuster Patent US. 3,199,698 issued Aug. 10, 1965.

It is an object of the invention to provide a control system which works primarily by fluid pressure, with attendant rugged reliability, and which provides for isolation of strictly electrical components of the system from the mechanical components thereof, whereby to greatly reduce the possibility of fouling the electrical components with lubricant, to provide for better accessibility, and to introduce other advantages.

It is a further object of this invention to provide an improved motion sensing device utilizing fiuid pressure creating and responsive mechanisms to achieve electric switch actuation in response to rotary motion.

Further objects and advantages will become apparent from the following description when read in conjunction with the drawings, in which:

FIG. 1 is a representation, partially diagrammatic in character, of a system involving the invention;

FIG. 2 is a vertical axial sectional view, with parts broken away, of one of the components of FIG. 1; and

FIG. 3 is a sectional view of the same taken on the line IIIIII of FIG. 2.

Referring to FIG. 1, the system is shown as applied to a lift truck which has a shaft permanently connected with the running gear or supporting wheels of the truck so as to rotate whenever the truck moves. Shaft 16 may also represent any kind of mechanism wherein it is desirable to sense the motion of a shaft or component for any purpose. Shaft 10 is shown as a component in the transmission of the truck, and has a gear 12 which meshes with an idler gear 14. The idler gear 14 in turn meshes with output gear 16 connected to an output shaft for driving the wheels of the lift truck. Gears 12 and 18 may be connected to the output shaft of an engine through a double clutch, not shown.

Shaft 10 drives a shaft 20, preferably of angular cross section, which is received in a fitting 22 fixed in relation to shaft 10, and which bridges the space between gear 12 and a fluid pump 24 carried in a wall 26 of the truck transmission. Shaft 20 is engaged in a complementary socket in a shaft 28 (see also FIG. 2) journaled in a boss 30 forming part of the body 31 of pump 24. It will be noted that shaft 28 is not centered in boss 30, but is offset so that it does not appear in FIG. 2 except in dotted lines. Suitable packing means 32 is provided to prevent loss of fluid about shaft 28.

Shaft 28 carries a gear 34, FIG. 3, fixed thereon, which meshes with a gear 36, both being enclosed in pump body 31 in the manner of the well known rotary gear pump.

, Such pumps are of the positive displacement type in that the fluid pumped must be allowed to flow when the pump is operated. If it is not, excessive pressure will be developed and the working parts or the pump will be blocked against movement,

A passageway 38 in body 31 extends from the space between and above the gears as seen in FIG. 3, into one end 40 of the displacement of cylinder 41 having a movable wall element or piston 42 therein, and a passageway 44 in body 31 extends from the space between and below gears 34 and 36 to the other end 45 of the displacement of cylinder 41, piston 42 having a fluid-tight sliding fit in bore 41 of cylinder 41, so that rotation of gears 34 and 36 in one direction, assuming pump 24 and cylinder 41 full of fluid, will remove fluid from one end of cylinder 41 and force it into the other, causing piston 42 to move. Piston 42 has a rod 46 which is of reduced diameter as compared with piston 42, and which extends outside of cylinder 41 through a suitable fluid-tight packing 48. A similar rod 50, identical in diameter with rod 46 is fixed to and extends in the other direction from piston 42 to the outside of cylinder 41 through a suitable packing 52 held in place by a head 53 fixed in any suitable manner on cylinder 41. In this way the displacement of piston 42 in chamber 41 is made equal to the displacement in chamber portion 45 so that the volume of fluid discharged from one end of cylinder 41, upon movement of piston 42, will be exactly equal to that required at the other end of cylinder 41 to fill the space vacated by the piston, as a result, no reservoir for fluid is necessary, and no allowance for volume variations is needed.

It will now be apparent that rotation of pump gears 34 and 36 in one direction will cause upward movement of piston 42, as seen in FIG. 2, while rotation of the gears in the opposite direction will cause downward movement of piston 42. It is to be understood that the terms up, down, etc., are used herein for convenience in describing the device, and that the components will work satisfactorily in any position, and can be so used.

A spring 54 serves to yieldingly maintain piston 42 in a predetermined central position in cylinder 41, hearing at one end upwardly against a washer 56 engaging a snap ring 58 fitted freely about a reduced portion 59 of rod 46, and engaged with a bushing 60, normally pressed upwardly against packing 48, and also with the shoulder 61 formed at the upper end of reduced portion 59. A head 62 is secured in any suitable manner on cylinder 41 and serves to withstand the pressure of packing 48, and to guide piston rod 46. At its other end spring 54 presses downwardly against a washer 64 seated on a shoulder 66 in cylinder 41, and also on the upper end of piston 42. Piston 42 is therefore held in place against upward movement by engagement with washer 64, and against downward movement by engagement of shoulder 61 with snap ring 58, although movement in either direction is permitted by yielding of spring 54. Upward movement will raise washer 64 off of shoulder and compress spring 54, while downward movement will move snap ring 58 and washer 56 downwardly away from bushing 60. Either movement will compress spring 54 and, conversely, extension of the spring will tend to maintain piston 42 in its predetermined central position.

Passageway 38 terminates in a port 68 in the wall of cylinder 41 positioned to be uncovered by piston 42 when approaching maximum upward travel as seen in FIG. 2 so as to open communication between passageways '44 and 38 so that the fluid coming from pump 24 is bypassed, thus allowing the pump to work without building up excessive pressure. In like manner passageway 44 terminates in a port 70 which is uncovered by piston 42 when approaching maximum downward travel, to also bypass the fluid coming from the pump when running in the reverse direction.

Piston rod 46 has fixed thereon a spool-like cam 72, in the present instance having opposed ramps 74 and 76, and a follower 78 in the form of a roller is seated between ramps 74 and 76 at such times as piston 42 is located in its predetermined position, as seen in FIG. 2. Follower 78 is carried on a lever arm 80 pivoted on a fulcrum 82 carried on a housing 84 containing suitable switching mechanism actuated by plunger 86 engaged with lever arm 80. Displacement of piston 42 and rod 46 in an upward direction will cause ramp 76 to press follower 78 to the left as seen in FIG. 1, swinging lever 80 to the dotted position and pressing plunger 86 to the left. This will actuate the switching mechanism, for example, from its open to its closed position, whereupon current will flow from a battery 88 through the switch and a lead 90 to a unit 92,

in the present instance a solenoid which closes a valve 94, blocking the flow of fluid from a pipe 96 to a pipe '98. The pipes would be so connected that such blocking would prevent flow of fluid out of the motor causing the clamping pressure in a lift truck load clamp as previously outlined, and thus prevent dropping of the load while the truck was in motion.

It is to be noted that downward movement of rod 45 will cause ramp 74 to force follower 78 toward the left in the same manner, so that the load cannot be dropped while the truck is in motion in either direction.

By reason of the spool-like shape of cam 72 the action on follower 78 will not be affected if piston 42. and rod 46 should tend to rotate as well as to move axially. Other types of cam are contemplated as within the scope of the invention.

Although described in connection with a lift truck, it is anticipated that the electric current, or interruption thereof, in lead 90 may be utilized for other purposes,

and in fact the motion of piston rod 46 could be used directly, without the intervention of electric switching mechanism, for sending a signal or controlling a mechanism, within the scope of the invention.

For purposes of manufacture, pump body 31 has a flange portion 100 which fits within .a socket 102 in a portion of cylinder 41, a ring nut 104 clamping the parts together. A suitable packing 106 prevents loss of fluid at the joint between the pump body and cylinder 41.

From the above it will be apparent that a system has been provided that will positively prevent dropping of the clamped load from a lift truck while the truck is in motion in either direction, and also that a system has been devised which can sense motion of a part in either direction, and transmit an appropriate signal. It will further be apparent that a device has been provided which will sense rotary motion in either direction and transform it to linear motion.

In operation, the device is filled with fluid, and in the event of rotation of shaft 10, pump 24 is caused to force fluid through passageways 38 and 44 in one and out the other, causing movement of piston 42. Suflicient movement of the piston will uncover one or the other of ports 68 and so that the pumped fluid may pass from one of ports 38 and 44 to the other, thus allowing pump 24, which otherwise would be blocked against movement, to operate without developing excessive pressure. Shifting of rod 46 in either direction will press follower 78 to the left and actuate the switch mechanism in housing 84, thereby transmitting a signal to unit 92, causing valve 94 to block the flow of fluid in pipes 96 and 98. This will prevent releasing of the clamps holding the load on the lift truck whenever the truck is in motion. When the vehicle is at rest the spring 54 will return the piston 42 to its neutral position shown in FIG. 2. This is made possible by building in internal leakage in the pump 24 and/ or hydraulic actuator. This is conveniently provided clusive property or privilege is claimed are defined as 41 in cylinder 41.

The embodiments of the invention for which an exby suitable clearance between the piston 42 and the bore follows:

1. In a control system for sensing rotation of a rotary part and transmitting a signal in response to such rotation, the combination comprising:

an electric switch having open and closed positions,

a fluid cylinder body having a displacement chamber,

a piston reciprocably disposed in and dividing said chamber into two portions at axially opposite sides of said piston and having a piston rod extending from said cylinder body,

means yieldably maintaining said piston in a predetermined position intermediate axially opposite ends of said chamber,

motion transmitting means on the portion of said rod extending from said cylinder body operative to actuate said switch upon a predetermined axial movement of said piston from its predetermined position,

a rotary positive displacement fluid pump for moving said piston having a pump body connected to said cylinder body,

a pumping element rotatably mounted in said pump body.

a drive shaft rotatably journaled in said pump body and drivingly interconnecting said pumping element and said rotary part, and

inlet and outlet passages in at least one of said bodies placing said pumping element in fluid receiving and delivery relationship with said chamber portions, respectively.

References Cited ROBERT K. SCHAEFER, Primary Examiner. 

